The present invention relates to an electrochemical capacitor, and more specifically relates to an electrochemical capacitor enclosing a rechargeable and dischargeable electric storage element in a film package.
An electrochemical capacitor such as electric dual layer capacitor, lithium ion capacitor, and redox capacitor is preferably uses a film package rather than a metal package as a capacitor body for productivity and cost benefits. Such a film package is generally formed rectangular from a laminate film including a protective layer, barrier layer, and seal layer. A typical conventional film package is formed by folding a rectangular laminate film with a predetermined size such that each half of the folded seal layer faces with one another and then heating the outer rim of the folded laminate film to fusion bond the opposing seal layers. Such film packages may also be formed from two separate rectangular laminate films with a predetermined size by overlapping the seal layers of each of the laminate films with one another and heating the outer rim of the overlapped laminate films to fusion bond the seal layers.
In order to provide a compact circuit, reflow-solderable electrochemical capacitors are desired. Reflow-solderable electrochemical capacitors may be mounted on a circuit board by reflow-soldering like other types of electronic components (e.g., chip capacitors or chip registers). Reflow-soldering leads to not only a much improved productivity of mounting process but also cost reduction.
However, such a film package used for an electrochemical capacitor is generally susceptible reflow-soldering process. There are several disadvantages with conventional film packages to be subjected to reflow-soldering process. Such disadvantages include leakage of electrolyte or gas out of the film package through the sealing section due to an increased inner pressure within the film package or due to softening or melting of the sealing section.
In order to overcome those disadvantages, it is proposed in Japanese Patent Application Publication 2000-223085 (the “'085 Publication”) to house a film package in a container to improve heat resistance of the film package. Another example to improve heat resistance of a film package is disclosed in Japanese Patent Application Publication 2009-182314 (the “'314 Publication”) where a film package is covered with a rigid material.
The container described in the '085 Publication can delay heat conduction to the film package. However, if a temperature profile for reflow-soldering has a prolonged heating period, the temperature of the film package in the container can rise near the peak temperature (e.g., 260-280° C.), which could result in leakage of electrolyte or gas out of the film package through the sealing section as with film packages without such a container.
The rigid material described in the '314 Publication also can delay heat conduction to the film package. However, if a temperature profile for reflow-soldering has a prolonged heating period, the temperature of the film package in the container can rise near the peak temperature (e.g., 260-280° C.), which could generate cracks in the rigid material and damage the film package due to increased inner pressure in the film package.